Extended bandwidth signal-to-noise ratio enhancement methods and means



ec. i6, 1969 c. R. TRIMBLE 3,484,59

EXTENDED BANDwITH sIGNAL-To-NoTsE RATIO ENHANCEMENT METHODS AND MEANS FLled July 18, 1966 3 Sheets-Sheet l Dec. 16, 1969 c. R. TRIMBLE EXTENDED BANDWITH SIGNAL-TONOISE RATIO ENHANCEMENT METHODS AND MEANS Filed July 18, 1966 Dec. 16, 1969 C. R. TRI'MBLE EXTENDED BANDwITH smNAL-To-NDISERATIO ENHANCEMENT METHODS AND MEANS 3 Sheets-Sheet 3 Filed July 18, 1966 o o E lo L ow R w n :awa a :awa 5 5@ w m. m 10 0 N T Auw oN AOV m 9;5 w m s 9 A a 2253 z E L T R 4 A Z252 E 22:02 z ozaz m EW 25 Q E 25 Smm Ez A A V A U v DNF n .F DE' 0.-' OF w A ov AGV U.S. Cl. 23S-152 15 Claims ABSTRACT OF THE DISCLOSURE A selected interval of a recurring input signal is repetitively sampled in amplitude at different time positions during m successive recurrences of the input signal to obtain X samples completely representing the selected input interval. This process is repeated during each of a plurality of signal averaging cycles. During the lfirst cycle the amplitude information obtained from each sample is stored as an average of one recurrence of the selected input interval in a memory location associated with the time position of that sample. During each succeeding cycle the difference in amplitude between each sample and the average stored in the associated memory location during the preceding cycle is divided by a selected factor and the resultant quotient signal employed as a correction factor to update that average.

This invention relates to methods and means for enhancing the signal-to-noise ratio of an electrical input having a high-frequency signal component so as to clearly differentiate that signal component from the noise component.

It is the principal object of this invention to provide methods and means for effectively extending the useful bandwidth of signal-to-noise ratio enhancement systems such as, for example, those disclosed in Clynes U.S. Patent 3,087,487 and in my own copending patent application Ser. No. 557,167, entitled Signal-to-Noise Ratio Enhancement Methods and Means and iiled on June 13, 1966.

The upper frequency limit of these systems is set by the minimum time interval T required for obtaining a data signal related to the amplitude of the input at a selected time position and for processing that data signal so as to provide a corresponding output display point. Accordingly, it is another object of this invention to provide sampling methods and means for making the effective data-pulse obtaining and processing time interval T represented by each output display point smaller than T so as to significantly increase this upper frequency limit. The upper frequency limit Amay be increased by as much as m, where m=T/'r. Since the sampling means determines how small -r can be made (the sample time lmust be short compared to 1- in order to approximate ideal sampling), the upper frequency limit may be extended to substantially the upper frequency limit of the sa-mpling means.

These objects are accomplished according to the illustrated embodiments of this invention by amplitude sampling m recurrences of a selected interval of a recurring input at the maximum sampling and processing rate 1/ T of the signal-to-noise ratio enhancement system so as to obtain X amplitude samples as required to completely represent the selected input interval. These X amplitude samples comprise what is hereinafter termed a sweep, and the amplitude samples obtained during each of the m recurrences of the selected input interval comprise what is hereinafter termed a pass. The average of a number of nited States Patent O 3,484,591 Patented Dec. 16, 1969 sweeps more accurately represents the signal vcomponent of the input than any single sweep because the signal component contributes consistently to the average while the unrelated noise component adds to or subtract's from the average randomly. Thus, a number of sweeps necessary to provide the desired signal-to-noise ratio enhancement are taken. After the rst pass 0f each sweep each subsequent pass is delayed relative to the preceding pass by one effective sampling and processing time interval, Fr=T/m, until the m passes have been taken and the sweep completed. Each amplitude sa-mple obtained during a sweep is processed so as to provide a related average signal which is stored in a memory location associated with the time position of that amplitude sample. An online, X point output display of the selected input interval is provided by driving a cathode ray tube in synchronism with this signal average process. The time interval represented by the output display of a sweep is merely XT, whereas the time interval required to take the sweep is XT (m times greater). l

Other' and incidental objects of this invention will become apparent from a reading of this specification and an inspection of the accompanying drawing in whih: t

FIGURE 1 is a block diagram illustrating an extended bandwidth signal-to-noise ratio enhancement system according to one embodiment of this invention; l

FIGURE 2 is a block diagram of a signal-to-noise ratio enhancement system according to another embodiment of this invention;

FIGURE 3 is a waveform diagram illustrating the operation of the systems yshown in FIGURES Land 2.

Referring to FIGURE 1v, there is shown feedback signal averageing means 10 for enhancing the signalto-noise ratio of an input having a signal-component' frequency sufficiently low that a sweep of amplitude samples can be obtained during a single pass of an input interval of interest. Time expansion means 12 is provided for extending the bandwidth of the signal averaging means n 10 by enabling it to make m passes of the selected input interval as required to obtain the sweep of amplitude samples. A recurring input waveform 14 (see FIGURE'iSa) having a high frequency signal component of interest-embedded in a heavy -background noise component is applied to a signal input 16 of the signal averaging means 10 at time To. Although any interval of this input waveform 14 from a portion of a recurrence to one or more recurrences may be selected for processing yand output display, a single recurrence is selected here for purposes of illustrating my invention. An externally generated synch pulse 18 (see FIGURE 3b) which is time locked to the input waveform 14 is applied to a synch input 20 of the time expansion means 12 at or before the beginning each of recurrence of the input waveform 14. As hereinafter described in detail, these synch pulses 18 are applied from the time expansion means 12 to the signal averaging means 10 for initiating each of the m passes of each sweep of the signal averaging process.

The feedback signal averaging means 10 may comprise, with wiring modifications to accommodate the time expansion means 12, stable averaging apparatus such as that shown and described in detail in my aforementioned copending patent application. A sample and hold circuit 22 is connected to the signal input 16 and is responsive to a train of timing pulses 24 (see FIGURE 3c) for sampling the input waveform 14 to produce an analog sample signal related to the amplitude of the input waveform at each sampling time position. A timer 26 is connected to the sample and hold circuit 22 `and is responsive to each synch pulse 18 that occurs at the beginning of the selected input interval for supplying a train of sample timing pulses 2-4 to the sample and hold circuit at the maximum sampling and processing rate l/T of the signal averaging means 10. Thus, (Y-l-l) amplitude samples are obtained during each pass of the selected input interval, where Y represents the largest integer in the absolute value of the quantity [(X-1)/m|.

A multiple channel -memory 28 comprising a series of memory locations, each of which is associated with a different sampling time position, is provided for storing the average amplitude information obtained by processing a sweep of amplitude samples. An address register 30 is connected to the memory 28 and is responsive to a timing pulse from the timer 26 for selecting the memory location associated with the time position of each amplitude sample as that sample is being taken and processed.

The signal averaging means operates to enhance the signal-to-noise ratio of the selected input interval by processing .each amplitude sample of a plurality of sweeps as generally indicated below for the Jth sample of the Nth sweep,A where the sample number is indicated by a superscript and the sweep number is indicated by a subscript. The memory 28 is connected to the timer 26 and is responsive to a timing pulse therefrom at a time TJ, the time position of the .lth amplitude sample, for supplying a digital average signal, MN 1J, to a digital-toanalog converter 32 and to an add or subtract circuit 34. This digital average signal represents the average amplitude information stored during the (N-l)th sweep in the Jth memory location selected by the address register 30 during processing of the Jth amplitude sample. It is zero when N is the first sweep. The digital-to-analog converter 32 converts this digital average signal to an equivalent analog average signal, MN 1J, and supplies it to one input of a differential amplifier 36. The sample and hold circuit 22 supplies the analog Jth amplitude sample signal, INJ, of the `Nth sweep to the other input of the differential amplier 36. An analog difference signal, INJ -MN 1J, indicating the difference between the amplitude sample signal, INJ, and the average signal, MN 1J, is thereby provided at the output of the differential amplifier 36.

A sweep counter 38 is connected to the timer 26 and is responsive to a timing pulse therefrom at time TN, the beginning of each sweep, for sequentially changing states to provide an output signal indicating the number of the sweep. The sweep counter 38 is connected for supplying the Nth sweep number output signal to a divide circuit 40. In response to a timing pulse from the timer 26 at time TJt1 this divide circuit 40 is set by the Nth sweep number output signal to divide a subsequently applied digital difference signal by N. An analog-to-digital converter 42 is connected to the differential amplifier 36 and is responsive to a timing pulse from the timer 26 at time TJ+2 for converting the analog difference signal, 1J -MN 1-7, to an equivalent digital difference signal. The analog-to-digital converter 42 is connected for supplying this digital difference signal to the divide circuit 40, which then produces a digital quotient signal, (INJ-MN 1J)/N. The dividecircuit 40 supplies this digital quotient signal to the add or subtract circuit 34. This add or subtract circuit 34 is responsive to a timing pulse from the timer 26 at time TH3 for algebraically adding the digital quotient signal, (INJ-MN 1J)/N, to the digital average signal, MN 1J, which was stored in the add or subtract circuit at time TJ. The output of the add or subtract circuit 34 is connected to the memory 28 for storing the resultant average signal, MNJ=MN 1J}- (INJ-MN 1J)/N, back in the Jth memory location when a timing pulse is supplied to the memory from the timer 26 at time TJ+4.

Processing each amplitude sample of each sweep in the above-described manner efficiently enhances the signal-to-noise ratio of the selected input interval of the waveform 14 by correcting during each sweep the average amplitude information stored in each memory location during the preceding sweep. Moreover, a full-scale, on-line output display of the selected input interval may be obtained by driving an oscilloscope 44 in synchronism with this signal averaging process as hereinafter described in detail.

The time expansion means 12 includes inhibit means comprising an AND gate 48 and a flip-flop 50 which are connected between the synch input 20 and a variabletime delay 52 to prevent extraneous synch pulses, such as may occur when the selected input interval comprises several recurrences of the input waveform 14, from interrupting a pass of the selected input interval once it is initiated. Thus, when the first synch pulse 18 (see FIGURE 3b) is passed through the AND gate 48, the fiip-flop 50 is set to an inhibit state for preventing subsequent synch pulses from passing through the AND gate until the pass initiated by the first synch pulse is com pleted.

The variable time delay circuit 52 is connected between the signal output of AND gate 48 and the timer 26 for delaying application of selected passed synch pulses 18 to the timer 26. A MOD m counter 54 is connected to the delay circuit 52 for varying its time delay at the end of each pass so that each passed synch pulse 18 after the first one is delayed by the effective sampling and processing time interval T relative to the preceding passed synch pulse 18 associated with the same sweep. The

' MOD m counter 54 counts the m passes of a sweep by changing states as follows, O, 1 m-l, 0, and accordingly varies the time delay of the delay circuit 52 so that the passed synch pulses 18 and, hence, the m passes of each sweep are successively delayed from the first to the mth pass by 0, r (m-1)1. Thus, the first passed synch pulse 18 passes without delay through the variable delay circuit 52 to the timer 26 for initiating the first pass of the first sweep. During this first pass the timer 26 supplies the first train of sample timing puls'e's 24 to the sample and hold circuit 22 for producing (Y-I-l) amplitude samples of the selected input interval at time positions spaced the minimum sampling and processing time interval T apart from the beginning of the selected input interval. The timer 26 is connected to an add m circuit 56 for supplying each train of sample timing pulses 24 thereto at the same time it is being supplied to the sample and hold circuit 22. This add m circuit 56 is connected to the address register 30 for incrementing the selected address of the address register by m in response to each of the applied sample timing pulses, except the first one of each sample timing pulse train 24. Thus, since the first memory location is initially selected to correspond to the 0 state of the MOD m counter 54, the resultant average signals obtained by processing the (Y-l-l) amplitude samples of the first pass are stored in the memory 28 in locations spaced m apart from the first memory location.

An overflow output of the add circuit 56 is connected to the timer 26, to the counting input of the MOD m counter 54, and to the flip-flop 50 for supplying an overiiow signal thereto after the last of the (Y-l-l) amplitude samples of each pass has been processed. This overfiow signal stops the train of sample timing pulses 24 being supplied to the sample and hold circuit 22 and reinitializes the timer 26 in preparation for the next passed synch pulse 18. It causes the MOD m counter 54 to change states so as to provide the variable delay circuit 52 with the appropriate time delay, for example, r when the MOD m counter changes from the 0 to the l state at the end of the first pass. Additionally, it sets the flip-flop 50 to a pass state so that the next synch pulse 18 applied to the AND gate 48 is passed to the variable delay circuit 52. The address register 30 is also connected to the overow output of the add m circuit 56 and to the output of the MOD m counter 54 for selecting a memory loca tion which corresponds to the new state of the MOD m counter in response to the overflow signal from the add m circuit, where the initially selected first memory location corresponds to the 0" MOD m counter state, the second memory location to the 1 MOD m counter state and the mth memory location to the m-l MOD m counter state.

The above-described cycle of operation is repeated in response to each of the subsequently passed vsynch pulses 18, which initiate the remaining m-l passes of the first sweep. Since the time delay between each subsequently passed synch'pulse 18 and the onset of the corresponding sample timing pulse train 24 is increased by .1- relative to the preceding time delay, by the end of the mth pass amplitude samples are taken of the selected input interval at X sampling time positions spaced spaced vapart. These amplitude samples are processed b y the signal averaging means 10 to provide corresponding resultant average signals which are interlaced into the memory 28 from the first to the Xth location in the order of increasing sample time position relative to the beginning of the selected input interval (see FIGURE 3d). The addresses of these X memory locations increase in the same order as the .memory locations. Thus, an on-line output display of the selected input interval (see FIGURE 3e) may be provided during the second sweep by driving an oscilloscope 44 in synchronism with' the signal averaging process. This is done by connecting the output of the digital-to-analog converter 32 for supplying each analog average signal to the vertical input of the oscilloscope 44 at the same time it is being supplied to the differential amplifier 36. A digital-to-analog converter S9 is connectedto the output of the address register 30 for converting each digital address, when that address is selected, toan analog address signal which is supplied to the horizontal input of the oscilloscope 44 as the time base for the corresponding analog average signal supplied to the vertical input by the digital-to-analog converter 32. During each pass the contents of (Y-l-l) different memory channels are read out in the order of increasing sample time position relative to the beginning of the selected input interval so as to form (Y-i-l) output display points 60 on the face of the cathode ray tube 61 of `the oscilloscope 44. Since the persistence of the cathode ray tube 61 is much longer than the time interval XT required to take and process a sweep of amplitude samples, all olf the X output display points60 are visible at the end of' the sweep. Thus, at the endfof the second sweep a full-'scale output display of the'@selectedv input interval is provided which does not change during the signal averaging process except to the extent of the attenuation of the noise component. Although an oscilloscope 44 is shown as the output device, virtually any analog or digital readout device may be used.

The MOD m counter 54 is connected to the timer 26 for supplying an overow signal thereto 'when the MOD m counter changes from the m-l to the state at the end of each sweep so as to reinitialize the timer in preparation for the next sweep which is taken in the same manner as the first sweep described above. A multiple position switch S8 is connected to the MOD m counter 54 and to the add m circuit 56 for selecting the value of m necessary to obtain a sweep of amplitude samples for the given high frequency input waveform 14. The m selection switch 58 may be constructed to permit selection of the value of m' from any one of a binary sequence of numbers such as 1, 2, 4, 8, 16 Alternatively, it may be constructed to permit selection of the value of m from any one of a decade sequence of numbers such as 1, 2, 4,10, 20 or 1, 2, 5,10, 20 for theconvenience of the operator. The selected value of m determines the value of r since the amplitude samples are taken and processed at the maximum rate l/T of the signal averaging means 10.

Referring now to FIGURE 2', there is shown feedback signal averaging means 62 which is constructed in the same manner as the signal averaging means shown in FIGURE 1, except for minor modifications as indicated to accommodate the new time expansion means 64. In accordance with these modifications the timer 26 is connected directly to the address register30 instead of first through the time expansion means, and the horizontal input of the oscilloscope 44 is connected to the time expansion means instead of to the output of the address register 30.v vThe signal averaging means 62 enhances the signal-to-noise ratiof` of the selected interval of the input waveform 14 (seeFIGURE 3a), which is applied to the signal input 16, in the same manner as described in connection with FIGURE l.

VThe time expansion means 64 includes inhibit means comprising an AND gate 48 and a Hip-flop 50 which are connected and which operate in the same manner as already shown and d escribed in connection with FIGURE l. Thus, synch pulses applied to the synch input 20 after a synch pulse 18'(see FIGURE 3b) is passed through the AND gate 48, to initiate a pass are prevented from interrupting that pass. A ramp generator 66 is connected to the output of the AND gate 48 and is triggered bv each passed synch pulse 18 to provide a ramp signal, the duration of which `varies with the value of m. An m selection switch 58' is connected to the ramp generator 66 and to a MOD m counter 54 for selecting the value of m necessary to obtain a sweep of X amplitude samples. This -m selection switch .58 controls the duration of the Iramp signal in accordance with the selected value of m so' that the ramp signal terminates after the (Y-l-l). amplitude samples of each pass have been taken. The ramp generator '66 supplies this ramp signal to lone input of a comparator 68. A digital-to-analog converter 70 is I connected for converting the digital vstate signal of the MOD m counter 54 to an equivalent analog signal which is supplied to the other input of the comparator 68. The comparator 68 supplies a pass-initiating signal to. the timer 26 when thelramp signal equals the analog signal representing the state of the lMOD m counter 54. This comparator inputl signal equivalence is made to occur at the start of the ramp signal when the MODv m counter 54 is in the "0 state, 'r later when it is in the "1 state and (m-1)r later when lit is in the (m-l) state. The MOD m'counter 54is initially lset to the 0" state. Thus. in response to the first passed synch pulse 18 thel timer 26 supplies the first train of sample timing pulses 24 (see FIGURE 3c) associated. with the first pass of the first sweep to the samplel and'hold'circuit 22 at vtime Tf.. the start of theramp sianaLThe sample and hold circuit 22 thereby produces (Y-l-l) amplitude `sarnples of the selectediinput interval at time positions spaced the minimum sampling and processing time T apart from the beginning of the selected input interval. Each sample timing pulse applied to the sample and hold circuit 22 is also applied to the address register 30 so that the resultant average signals obtained by processing the (Y-l-l) amplitude samples of the first pass are consecutivelv stored in the first (Y-l-l) locations of the memory 28 (see FIGURE 3 f).

The ramp generator 66 is connected to the timer 26, to the counting input of the MOD m counter 54, and to the fiip-flop 50 for supplying a control signal thereto upon termination of the ramp signal after the last of the Y-l-l) amplitude samples of a pass have been processed. This control signal stops the train of sample timing pulses 24 being supplied to the sample and hold circuit 22 and reinitializes the timer 26 in preparation for the next passed synch pulse 18. It causes the MOD m counter S4 to change states so that the comparator input signal equivalence required for the comparator 68 to initiate the next pass of the sweep occurs r later than it did for the preceding pass. Additionally, it sets the ffip-fiop S0 to a pass state so that the next synch pulse applied to the AND gate 48 is passed to initiate the next pass of the sweep.

The above-described cycle of operation is repeated in response to each of the subsequently passed synch pulses 18, which initiate the remaining m-l passes of the first sweep. iSince the time -delay between each subsequently passed synch pulse 18.and the onset of the corresponding sample timing pulse train 24 is increased by -r relative the preceding time delay, by the end of the mth pass amplitude samples are taken of the selected input interval at X sampling time positions spaced T apart. These amplitude samples are processed by the signal averaging means 62 to produce resultant average signals which are sequentially stored in the memory 28 from the rst to the Xth memory location in the order they are taken (see FIGURE 3f). The MOD m counter 54 is connected to the timer 26 for supplying an overow signal thereto when the MOD m counter changes from the "m1 state to the state at the end of each sweep so as to reinitialize the timer in preparation for the next sweep which is taken in the same manner as the first sweep described above.

The output of the ramp generator 66 is connected to the horizontal input of the oscilloscope 44 for supplying the ramp signal thereto as the time base for the analog average signals that are supplied to the vertical input of the oscilloscope during the associated pass. However, since all amplitude samples are processed and sequentially stored in the X memory locations, the memory 28 must be decoded for readout. This may be done by Z-axis modulation of the oscilloscope 44 in which the vertical input is blanked until an unblanking signal is applied to the Z-axis input. An on-line output display of the selected input interval (see FIGURE 3g) is obtained by connecting the output of the comparator 68 through a delay circuit 72 to the Z-axis input of the oscilloscope 44 so as to provide this unblanking signal to the Z-axis input when processing of the rst amplitude sa-mple of each pass is completed. During each pass the contents of (Y-I-l) different memory locations are read out in the order of increasing sample time position relative to the beginning of the selected input interval until all of the X output display points 60 are obtained. Thus, by the end of the mth pass of the second sweep a full-scale output display (See FIGURE 3g) comprising X output display points 60 is obtained. The readout problem becomes more complex if the output device is to be a printer or an X-Y recorder instead of an oscilloscope. In this case an address decoding network must be used to map the real time at which each resultant average signal is stored in a memory location onto the expanded time scale. One method of doing this is to use the interlace technique for loading the memory locations as described above in connection with FIGURE 1. I claim: 1. A method for enhancing the signal-to-noise ratio of a selected interval of a recurring input, comprising the steps of i sampling a plural number m of recurrences of the selected input interval to produce X sample signals, each of which is related to the amplitude of the selected input interval at a different time position therein; storing information related to said X sample signals in X memory locations, each of which is associated with a different one of said time positions;

repeating said sampling and storing steps to provide in said X memory locations resultant information related to said sample signals; and

reading out said resultant information stored in said X memory locations to provide an output in which the signal-to-noise ratio of the selected input interval is enhanced.

2. A method as in claim 1 wherein said storing step comprises storing information related to the sample signals produced by sampling the same one of said m recurrences in said X memory locations m locations apart beginning with the memory location associated with the time position of the first sample signal produced by sampling said one recurrence.

3. A method as in claim 1 wherein:

said storing step comprises storing said information in said X memory locations from the iirst to the Xth memory location in the order in which said X sample signals are taken; and

said reading step comprises reading out said resultant information stored in each of said X memory loca-` tions at a time related to the order of said time positions in the selected input interval.

4. A method as in claim 1 wherein said storing step comprises the substeps of:

processing each of said sample signals to produce a corfrection signal related to the difference between the sample signal and any information previously stored in the memory location associated with the time position of the same sample signal; and

algebraically adding said correction signal to any information previously stored in the memory location associated with the time position of the same sample signal.

5. Apparatus for enhancing the signal-to-noise ratio of 20 a selected interval of a recurring input, comprising:

sampling means for repetitively sampling the selected input interval to produce during each of N successive Vsets of m recurrences thereof X sample signals, each of which is related to the amplitude of the selected input interval at a different time position therein;

memory means including X memory locations, each of which is associated with a different one of said time positions;

circuit means connecting said sampling means to said memory means for storing in said X memory locations information related to said X sample signals produced by sampling each of said sets to provide in said X memory locations resultant information related to said NX sample signals; and

' output means connected to said memory means for reading out said resultant information stored in said X -memory locations to provide an output in which the signal-to-noise ratio of the selected input interval is enhanced.

6. Apparatus as in claim wherein said sampling means comprises:

a sampling circuit for repetitively sampling the selected input interval; and

delay means connected to said sampling circuit for delaying during each of said N sets the sampling of each recurrence following the first one of the set by a selected time interval relative to the sampling of the preceding recurrence of the same set to produce said X sample signals.

7. Apparatus as in claim 6 wherein:

said delay means includes selection means for alter ably selecting said number m to determine said se lected time interval; and

said circuit means includes processing means for proc-- essing each of said sample signals to produce a correction signal related to the difference between the sample signal and any information previously stored in the memory location associated with the time position of the same sample signal and for algebraically adding the correction signal to any information previously stored in the `memory location associated With the time position of the same sample signal.

8. Apparatus as in claim 6 wherein said circuit means stores said information related to the sample signals produced by sampling the same one of said m recurrences of the same one of said N sets in said X memory locations m locations apart beginning with the memory location as sociated with the time position of the rst sample signal produced by sampling said one recurrence.

9. Apparatus as in claim 6 wherein:

said circuit means stores said information related to said X sample signals produced during said sampling 0f each 0f Said Sets irl Said X memory locations from the first to the Xth memory location in the order in which said X, sample signals are taken; and

said output means includes decoding meansffor timerelating the `ifeadout of said resultant information stored in said-X memory locations to said time positions in the selected input interval.

10. Apparatus s in claim 6 wherein said output means includes a cathod` ray tube circuit for reading out, during each of said recurrences of selected ones of said N sets, the information stored in selected ones of said X memory channelsj; in the order of increasing tiniie position relative to the beginning of the selected input interval.`

11. Apparatus as in claim 6 wherein said circuit means comprises:

difference means connected to said sampling means and to said memory Imeans for producing aditference signal related to the dilerence between each sample signal and 'zi-lily information previously stored in the memory location associated with the time'position of that sample'signal; and

means connected to said difference means and to said memory means for dividing each difference signal by a selected factor and for algebraically adding the resulting vquotient to any information 'prleviously stored in t'ljie memory location associated with the time position of the sample signal from which that quotient wallsin part derived. j'

12. Apparatus for enhancing the signal-to-,noise ratio of a selected interval of a recurring input, said apparatus comprising:

first means fory processing a plurality of recurrences of the selectedinput interval to produce for each recurrence lprocessed X/m data signals related to the amplitude of the selected input interval at X/ m different time positions therein;

second meanslconnected to said first means and operable for delaying the processing of eachfrecurrence followinglthe first one in each of N sets ,of4 m recurrences ofthe selected input interval by' a selected time interval relative to the processing of the preceding recurrence of the same set so that said'irst means produces ,X data signals related to the amplitude of the selected input interval at X different time positions theein for each of said N sets; j

third means including X storage locations, each of said X storage locations being associated with a different one of said X time positions in the selected input intervalf fourth means connected to said iirst and third means and operable for storing in said X storage locations of said third means information related to said X storage data signals produced by said first means :for

each of said N sets to provide n said X storage locations resultant information related to said NX data signals; and iifth means connected to said third means and responsive to the resultant information stored in said X storage locations ,to provide an output in which the signal-to-noise ratio of the selected input interval is enhanced. ,f 13. Apparatus as in claim 12 wherein said fourth means stores saidy information related to the X/ midata signals produced= by processidg the same one of s'ziid m recurrences of the same one of said N sets m: locations apart in said Xstorage locations of said third means."

14. Apparatus as infclaim 12 wherein: said fourth means stores said information related to the X/m data signals produced by processing the same one of saidljml recurrences of the',fsame one of said N sets in said-X storage locations from the first to the Xth storage-location in the order in which said X data signals are'iuroduced; and said fifth means' includes 'means for time relating the yresultant information stored in said X storage locations to the orderof said X time positions in the selected input interval so that in said output the resultant information is indicated in the'forder of increasing time pos'itlion relative to the beginning of the selected input interval. 15. Apparatus as in claim 12 wherein said fourth means comprises: sixth means connected to said first means and to said third means and operable for producing a difference signal related to (the difference between each data signal and any information previously stored in the storage location asfsociated with the time position of that data signal; and seventh means connected to said sixth means and to said third means and operable for dividing cach difference signal by selected factor and for algebraically adding the resulting quotient an any information previously stored in the storage location associated with the time position of the data signal from which that quotient was in part derived..

References Cited :l UNITED srATEs PATENTS Uys. c1a Xn.. 12s- 2.1; 324-417 

